镁铁—超镁铁岩的分类及其构造意义

Classifications of mafic-ultramafic rocks and their tectonic significance

镁铁—超镁铁岩分类是镁铁—超镁铁岩研究最基本的问题之一。镁铁—超镁铁岩(不包括金伯利岩、煌斑岩和碱性超镁铁岩等)按照产出的构造背景、岩石组合、伴生矿产大体可分为5类,即:蛇绿岩、义敦型岩体、阿拉斯加型岩体、层状侵入体和橄榄岩—闪长岩型岩体。蛇绿岩代表大洋岩石圈地幔及其分异物;义敦型代表大陆岩石圈地幔及其分异物;阿拉斯加型岩体来自岛弧、活动陆缘环境或具岛弧之下地幔特征的源岩;层状侵入体来自板内伸展构造背景;橄榄岩一闪长岩型岩体的构造背景与阿拉斯加型类似,但是也有产于板内环境的。蛇绿岩是学术界最关注的问题之一,笔者认为,1972年彭罗斯会议确定的蛇绿岩的定义仍然是适用的,斯泰因曼三位一体的概念仍然是有效的,而Delik的蛇绿岩定义和分类是不可取的。笔者认为,义敦型的概念是合适的和有用的。蛇绿岩与义敦型岩体有许多相似之处,但是,它们的构造含义不同。它们之间的区别不是依靠岩石组合本身,也不依靠地球化学,而是依靠野外产出位置和伴生的围岩性质以及构造情况。不同类型的镁铁一超镁铁岩形成的构造背景不同,伴生的矿产类型不同,具有不同的大地构造意义。在野外实践和室内研究中注意它们之间的区别,无论对于理论研究还是找矿研究都是非常重要的。

The classification of the mafic-uhramafic rocks is one of the basic problems in the research of the mafic-ultramafic rocks. The mafic-ultramafic rocks （ exclude the kimberlite, lamprophyre and alkaline ultramafic rock, etc） can be divided into five types by the output tectonic background, rock suit and associated minerals. They are ophiolite, Yidun-type, Alaskan-type, layered intrusive type and peridotite-diorite type. The ophiolites represent ocean lithosphere mantle and its products of evolution. The Yidun-type represents the continental lithosphere mantle and its different products. The source rocks of the Alaskan-type are from island arc, epicontinental environment or with under arc characteristics of mantle. The layered intrusive type is from plate extensional tectonic setting. The peridotite-diorite type have similar tectonic background with Alaskan-type, but they are also found in intraplate environment. Ophiolite is one of the most concerned problems in academia, the author thinks that, the definition of ophiolite established in Penrose meeting of 1972 is still applicable and the concept of the Steinmann trinity is still effective. While the definition and classification made by Delik is not desirable. The author also thinks that the concept of Yidun-type is appropriate and useful. The ophiolite and Yidun-type have many similarities, but they have different meanings. The differences between them do not rely on rock suit or geochemistry, but rely on field output position and properties and structure of associated wall rocks. Different mafic-uhramafic rocks have different tectonic settings, and the associated deposit types and geotectonic significance are different. No matter in the field and laboratory study, paying attention to the differences between them is very important both in theoretical research and prospecting research.